A conventional LARP (“Laser Activated Remote Phosphor”) light source has a converter layer for converting primary light of a first spectral composition into secondary light of a second spectral composition is irradiated with primary light in the form of laser light. The converter layer then emits only secondary light or a mixture of the converted secondary light and non-converted primary light. LARP light sources have the advantage that in conjunction with a compact construction they can generate high luminous fluxes with at the same time high luminance. In this case, so-called reflective arrangements are usually used for generating particularly high luminous fluxes and luminances, in which arrangements the emitted light, e.g. the mixed light, is emitted from the same side of the converter layer at which the primary light is also incident. In order to obtain a high conversion efficiency and to prevent light from emerging at the rear side of the converter facing away from the irradiated side, a mirror is typically fitted at the rear side. The mirror reflects light emerging from the rear side of the converter back into the converter.
However, in the case of such LARP light sources, high thermal loadings, e.g. cyclic alternating loads, can occur at the converter and can lead to damage or even to failure (e.g. detachment) of the converter. In that case an amount of primary light harmful to human beings may possibly be coupled into a useful light path without being noticed, e.g. primary light reflected at detached particles or even directly from the mirror. It is particularly disadvantageous here if, in the event of a mechanical fracture, reflectively coated fragments of the mirror pass into the beam path.
In order to monitor a mechanical integrity of the converter with reflective arrangement, hitherto it has been known to monitor a ratio of the proportions of primary light and secondary light in the mixed light in the useful light path. This exploits the fact that the ratio may change as a result of damage to the converter layer. However, disadvantageously, such monitoring is not particularly reliable.
Moreover, it is known to use beam traps that block primary light which has not penetrated into the converter but has been reflected at particles. What is disadvantageous here is that space has to be additionally provided for this and, what is more, primary light that is reflected in this way and follows the useful light path is not blocked.